Composite semipermeable membrane and process for producing the same

ABSTRACT

The present invention aims at providing a composite semipermeable membrane in which water permeability and salt-blocking rate cannot deteriorate by long-term storage, and at providing a process for producing the same. The present invention relates to a composite semipermeable membrane having a skin layer formed on the surface of a porous support, the skin layer including a polyamide resin obtained by interfacial polymerization of a polyfunctional amine component and a polyfunctional acid halide component, wherein the porous support contains at least one kind of additives selected from the group consisting of antioxidants, antibacterial agents, antifungal agents, and moisturizers, in an amount of 95% by weight or more with respect to the whole composite semipermeable membrane.

FIELD OF THE INVENTION

The present invention relates to a composite semipermeable membranehaving a skin layer which includes a polyamide resin and a poroussupport that supports the skin layer, and to a process for producing thecomposite semipermeable membrane. The composite semipermeable membranesare suitably used for production of ultrapure water, desalination ofbrackish water or sea water, etc., and usable for removing or collectingpollution sources or effective substances from pollution, which causesenvironment pollution occurrence, such as dyeing drainage andelectrodeposition paint drainage, leading to contribute to closed systemfor drainage. Furthermore, the membrane can be used for concentration ofactive ingredients in foodstuffs usage, for an advanced water treatment,such as removal of harmful component in water purification and sewageusage etc.

DESCRIPTION OF THE RELATED ART

Recently, a composite semipermeable membrane, in which a skin layerincludes polyamides obtained by interfacial polymerization ofpolyfunctional aromatic amines and polyfunctional aromatic acid halidesand is formed on a porous support, has been proposed (Patent Document1). A composite semipermeable membrane, in which a skin layer includes apolyamide obtained by interfacial polymerization of a polyfunctionalaromatic amine and a polyfunctional alicyclic acid halide and is formedon a porous support, has been also proposed (Patent Document 2).

However, when it is needed to obtain a target compounds condensed orrefined as permeated liquid or non-permeated liquids using conventionalcomposite semipermeable membranes in actual cases, there has occurred aproblem of unstable water quality of target compounds due todeterioration with time of performances, such as water permeability andsolute blocking property, of the composite semipermeable membranes.

On the other hand, from viewpoints of subsequent workability,preservability, etc., the composite semipermeable membrane produced ispreferably a dried composite semipermeable membrane. However, when acomposite semipermeable membrane having a skin layer formed on thesurface of the porous support is dried, there has occurred a problem ofdeterioration of salt-blocking performance and permeation flux, comparedwith characteristics before drying. A technique in which a reverseosmosis membrane is dried after hydrophilization treatment for thepurpose of solving the problem has been disclosed (Patent Document 3).Furthermore, a method of drying a composite membrane after immersiontreatment in a solution of saccharides having a molecular weight of 1000or less has been disclosed (Patent Document 4).

In order to obtain a dried composite reverse osmosis membrane havingoutstanding water permeability, organic matter blocking performance, andsalt-blocking performance, a method of performing heat drying treatmentof a compound reverse osmosis membrane after contact to an aqueoussolution at a temperature of 40 to 100° C. has been disclosed (PatentDocument 5).

However, various kinds of above-described treatments, for the purpose ofcontrol of deterioration of the performance and quality, applied to acomposite semipermeable membrane having a skin layer formed on thesurface of a porous support conversely promotes deterioration ofsalt-blocking performance and permeation flux depending on kinds ofchemicals used, treatment method, etc., in some case.

[Patent Document 1] Japanese Patent Application Laid-Open No. 02-187135

[Patent Document 2] Japanese Patent Application Laid-Open No. 62-121603

[Patent Document 3] Japanese Patent Application Laid-Open No.2003-320224

[Patent Document 4] Patent No. 3015853 specification

[Patent Document 5] Japanese Patent Application Laid-Open No. 10-165789

SUMMARY OF THE INVENTION

The present invention aims at providing a composite semipermeablemembrane in which water permeability and salt-blocking rate cannotdeteriorate by long-term storage, and at providing a process forproducing the same.

As a result of wholehearted investigation conducted by the presentinventors for attaining the above-described objectives, it has beenfound out that inclusion of specific additives in a porous support afterformation of a skin layer can provide a composite semipermeable membranein which water permeability and salt-blocking rate cannot deteriorateafter long-term storage, leading to completion of the present invention.

That is, the present invention relates to a composite semipermeablemembrane having a skin layer formed on the surface of a porous support,the skin layer including a polyamide resin obtained by interfacialpolymerization of a polyfunctional amine component and a polyfunctionalacid halide component, wherein the porous support contains at least onekind of additives selected from the group consisting of antioxidants,antibacterial agents, antifungal agents, and moisturizers, in an amountof 95% by weight or more with respect to the whole compositesemipermeable membrane.

Reasons for deterioration with time of performances, such as waterpermeability and solute blocking property, of a composite semipermeablemembrane include possible degradation of the composite semipermeablemembrane by increase of bacillus, appearance of mold, structural changeby drying at the time of storage, and chemical change by oxidation, etc.

Furthermore, various treatments, as applied in various treatments forconventional composite semipermeable membranes, by entire immersion,etc., of the composite semipermeable membranes with a flat film form orwith a processed spiral element form allow expression of objectivefunction by the treatment agent, but at the same time the treatmentpossibly gives unpreferable modification, such as swelling, hydrolysis,denaturation, etc., to the skin layer, and some treatment measure maygive physical damage to the skin layer. Such possibilities areconsidered to be one of the causes of degradation of the compositesemipermeable membrane.

The composite semipermeable membrane of the present invention ischaracterized by including the above-described additives mainly in theporous support. For this reason, the composite semipermeable membrane ofthe present invention can minimize secondary adverse effect to the skinlayer, and can exhibit characteristics of giving no deterioration inwater permeability and salt-blocking rate by long-term storage withoutdeterioration of performance of the skin layer.

The composite semipermeable membrane of the present invention ispreferred to be a dried composite semipermeable membrane from viewpointsof workability, preservability, stability of quality and performance.

In the present invention, moisturizers are preferably of organic acidmetal salts and/or inorganic acid metal salts.

The organic acid metal salt preferably include at least one kind oforganic acid alkali metal salt selected from the group consisting ofalkali metal acetate, alkali metal lactate, and alkali metal glutamate.The alkali metal is preferably selected from sodium or potassium.

In addition, the inorganic acid metal salt preferably includes at leastone kind of inorganic acid alkali metal salt selected from the groupconsisting of alkali metal hydrogencarbonate, dialkali metalmonohydrogen phosphate, monoalkali metal dihydrogen phosphate, Thealkali metal is preferably selected from sodium or potassium.

Although a prolonged moisturing treatment is needed in order to obtainnecessary effect when using as surfactants and saccharides as amoisturizer, use of the organic acid metal salts and/or inorganic acidmetal salts can give sufficient effect by extremely short-timemoisturing treatment, leading to great advantage on the productiveprocess. In addition, although use of the surfactants or saccharides asa moisturizer may give poor effect depending on drying conditions(temperature, period of time, etc.), use of the organic acid metal saltsand/or inorganic acid metal salts can provide sufficient effectindependently of dry conditions, resulting in great advantage on theproductive processes.

The present invention also relates to a process for producing acomposite semipermeable membrane comprising the steps of: forming a skinlayer including a polyamide resin obtained by reaction between apolyfunctional amine component and a polyfunctional acid halidecomponent on the surface of a porous support; and performing a treatmentwith additives onto the porous support by contact of an aqueous solutionincluding at least one kind of additives selected from the groupconsisting of an antioxidant, an antibacterial agent, an antifungalagent, and a moisturizer, to a face without the skin layer of the poroussupport.

BEST MODE FOR CARRYING OUT OF THE INVENTION

The embodiments of the invention will, hereinafter, be described. In thecomposite semipermeable membrane of the present invention, a skin layercontaining a polyamide resin obtained by interfacial polymerization of apolyfunctional amine component and a polyfunctional acid halidecomponent is formed on the surface of a porous support, and the poroussupport contains at least one kind of additives selected from the groupconsisting of antioxidants, antibacterial agents, antifungal agents, andmoisturizers in an amount of 95% by weight or more with respect to thetotal weight of the composite semipermeable membrane.

The polyfunctional amine component is defined as a polyfunctional aminehaving two or more reactive amino groups, and includes aromatic,aliphatic, and alicyclic polyfunctional amines.

The aromatic polyfunctional amines include, for example,m-phenylenediamine, p-phenylenediamine, o-phenylenediamine,1,3,5-triamino benzene, 1,2,4-triamino benzene, 3,5-diaminobenzoic acid,2,4-diaminotoluene, 2,6-diaminotoluene,N,N′-dimethyl-m-phenylenediamine, 2,4-diaminoanisole, amidol, xylylenediamine etc.

The aliphatic polyfunctional amines include, for example,ethylenediamine, propylenediamine, tris(2-aminoethyl)amine,n-phenylethylenediamine, etc.

The alicyclic polyfunctional amines include, for example,1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane,piperazine, 2,5-dimethylpiperazine, 4-aminomethyl piperazine, etc.

These polyfunctional amines may be used independently, and two or morekinds may be used in combination. In order to obtain a skin layer havinga higher salt-blocking property, it is preferred to use the aromaticpolyfunctional amines.

The polyfunctional acid halide component represents polyfunctional acidhalides having two or more reactive carbonyl groups.

The polyfunctional acid halides include aromatic, aliphatic, andalicyclic polyfunctional acid halides.

The aromatic polyfunctional acid halides include, for example trimesicacid trichloride, terephthalic acid dichloride, isophthalic aciddichloride, biphenyl dicarboxylic acid dichloride, naphthalenedicarboxylic acid dichloride, benzenetrisulfonic acid trichloride,benzenedisulfonic acid dichloride, chlorosulfonyl benzenedicarboxylicacid dichloride etc.

The aliphatic polyfunctional acid halides include, for example,propanedicarboxylic acid dichloride, butane dicarboxylic aciddichloride, pentanedicarboxylic acid dichloride, propane tricarboxylicacid trichloride, butane tricarboxylic acid trichloride, pentanetricarboxylic acid trichloride, glutaryl halide, adipoyl halide etc.

The alicyclic polyfunctional acid halides include, for example,cyclopropane tricarboxylic acid trichloride, cyclobutanetetracarboxylicacid tetrachloride, cyclopentane tricarboxylic acid trichloride,cyclopentanetetracarboxylic acid tetrachloride, cyclohexanetricarboxylicacid trichloride, tetrahydrofurantetracarboxylic acid tetrachloride,cyclopentanedicarboxylic acid dichloride, cyclobutanedicarboxylic aciddichloride, cyclohexanedicarboxylic acid dichloride, tetrahydrofurandicarboxylic acid dichloride, etc.

These polyfunctional acid halides may be used independently, and two ormore kinds may be used in combination. In order to obtain a skin layerhaving higher salt-blocking property, it is preferred to use aromaticpolyfunctional acid halides. In addition, it is preferred to form across linked structure using polyfunctional acid halides havingtrivalency or more as at least a part of the polyfunctional acid halidecomponents.

Furthermore, in order to improve performance of the skin layer includingthe polyamide resin, polymers such as polyvinyl alcohol,polyvinylpyrrolidone, and polyacrylic acids etc., and polyhydricalcohols, such as sorbitol and glycerin, may be copolymerized.

The porous support for supporting the skin layer is not especiallylimited as long as it has a function for supporting the skin layer, andusually ultrafiltration membrane having micro pores with an average poresize approximately 10 to 500 angstroms may preferably be used. Materialsfor formation of the porous support include various materials, forexample, polyarylether sulfones, such as polysulfones and polyethersulfones; polyimides; polyvinylidene fluorides; etc., and polysulfonesand polyarylether sulfones are especially preferably used from aviewpoint of chemical, mechanical, and thermal stability. The thicknessof this porous support is usually approximately 25 to 125 μm, andpreferably approximately 40 to 75 μm, but the thickness is notnecessarily limited to them. The porous support may be reinforced withbacking by cloths, nonwoven fabric, etc.

Processes for forming the skin layer including the polyamide resin onthe surface of the porous support is not in particular limited, and anypublicly known methods may be used. For example, the publicly knownmethods include an interfacial condensation method, a phase separationmethod, a thin film application method, etc. The interfacialcondensation method is a method, wherein an amine aqueous solutioncontaining a polyfunctional amine component, an organic solutioncontaining a polyfunctional acid halide component are forced to contacttogether to form a skin layer by an interfacial polymerization, and thenthe obtained skin layer is laid on a porous support, and a methodwherein a skin layer of a polyamide resin is directly formed on a poroussupport by the above-described interfacial polymerization on a poroussupport. Details, such as conditions of the interfacial condensationmethod, are described in Japanese Patent Application Laid-Open No.58-24303, Japanese Patent Application Laid-Open No. 01-180208, and theseknown methods are suitably employable.

In the present invention, it is especially preferred that a coveringlayer of aqueous solution made from the amine aqueous solutioncontaining a polyfunctional amine components is formed on the poroussupport, then an interfacial polymerization is performed by contact withan organic solution containing a polyfunctional acid halide component,and the covering layer of aqueous solution, and then a skin layer isformed.

In the interfacial-polymerization method, although the concentration ofthe polyfunctional amine component in the amine aqueous solution is notin particular limited, the concentration is preferably 0.1 to 5% byweight, and more preferably 0.5 to 2% by weight. Less than 0.1% byweight of the concentration of the polyfunctional amine component mayeasily cause defect such as pinhole. in the skin layer, leading totendency of deterioration of salt-blocking property. On the other hand,the concentration of the polyfunctional amine component exceeding 5% byweight allows easy permeation of the polyfunctional amine component intothe porous support to be an excessively large thickness and to raise thepermeation resistance, likely giving deterioration of the permeationflux.

Although the concentration of the polyfunctional acid halide componentin the organic solution is not in particular limited, it is preferably0.01 to 5% by weight, and more preferably 0.05 to 3% by weight. Lessthan 0.01% by weight of the concentration of the polyfunctional acidhalide component is apt to make the unreacted polyfunctional aminecomponent remain, to cause defect such as pinhole in the skin layer,leading to tendency of deterioration of salt-blocking property. On theother hand, the concentration exceeding 5% by weight of thepolyfunctional acid halide component is apt to make the unreactedpolyfunctional acid halide component remain, to be an excessively largethickness and to raise the permeation resistance, likely givingdeterioration of the permeation flux.

The organic solvents used for the organic solution is not especiallylimited as long as they have small solubility to water, and do not causedegradation of the porous support, and dissolve the polyfunctional acidhalide component. For example, the organic solvents include saturatedhydrocarbons, such as cyclohexane, heptane, octane, and nonane,halogenated hydrocarbons, such as 1,1,2-trichlorofluoroethane, etc. Theyare preferably saturated hydrocarbons having a boiling point of 300° C.or less, and more preferably 200° C. or less, or naphthene solvents.

Various kinds of additives may be added to the amine aqueous solution orthe organic solution in order to provide easy film production and toimprove performance of the composite semipermeable membrane to beobtained. The additives include, for example, surfactants, such assodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and sodiumlauryl sulfate; basic compounds, such as sodium hydroxide, trisodiumphosphate, triethylamine, etc. for removing hydrogen halides formed bypolymerization; acylation catalysts; compounds having a solubilityparameter of 8 to 14 (cal/cm³)^(1/2) described in Japanese PatentApplication Laid-Open No. 08-224452.

The period of time after application of the amine aqueous solution untilapplication of the organic solution on the porous support depends on thecomposition and viscosity of the amine aqueous solution, and on the poresize of the surface layer of the porous support, and it is preferably 15seconds or less, and more preferably 5 seconds or less. Applicationinterval of the solution exceeding 15 seconds may allow permeation anddiffusion of the amine aqueous solution to a deeper portion in theporous support, and possibly cause a large amount of the residualunreacted polyfunctional amine components in the porous support. In thiscase, removal of the unreacted polyfunctional amine component that haspermeated to the deeper portion in the porous support is probablydifficult even with a subsequent membrane washing treatment. Excessiveamine aqueous solution may be removed after covering by the amineaqueous solution on the porous support.

In the present invention, after the contact with the covering layer ofaqueous solution and the organic solution including the amine aqueoussolution, it is preferred to remove the excessive organic solution onthe porous support, and to dry the formed membrane on the porous supportby heating at a temperature of 70° C. or more, forming the skin layer.Heat-treatment of the formed membrane can improve the mechanicalstrength, heat-resisting property, etc. The heating temperature is morepreferably 70 to 200° C., and especially preferably 100 to 150° C. Theheating period of time is preferably approximately 30 seconds to 10minutes, and more preferably approximately 40 seconds to 7 minutes.

The thickness of the skin layer formed on the porous support is not inparticular limited, and it is usually approximately 0.05 to 2 μm, andpreferably 0.1 to 1 μm.

In the present invention, a washed composite semipermeable membrane maybe obtained by subsequently applying membrane washing treatment to theproduced composite semipermeable membrane. The method of the membranewashing treatment is not in particular limited, and conventionallypublicly known methods are employable. The following membrane washingtreatment is especially preferably adopted.

1) Method of washing the membrane by contact of the compositesemipermeable membrane with pure water or ion exchange water.

2) Method of washing the membrane by contact of the compositesemipermeable membrane with an aqueous solution containing an acidicsubstance and/or an inorganic salt, and an water-soluble organicsubstance.

The acidic substance concerned is not in particular limited as long asit is water-soluble, and for example, inorganic acids, such ashydrochloric acid, sulfuric acid, and phosphoric acid; organic acids,such as formic acid, acetic acid, and citric acid, may be mentioned.

The inorganic salt is not in particular limited as long as it is ainorganic salt that can form a complex with an amido group and, forexample, lithium chloride (LiCl), calcium chloride (CaCl₂), rhodancalcium [Ca(SCN)₂], and rhodan potassium (KSCN) may be mentioned.

The concentration of the acidic substance and/or the mineral salt in theaqueous solution is preferably 10 ppm to 50% by weight, more preferably50 ppm to 20% by weight, and especially preferably 1 to 10% by weight.The concentration of the acidic substance and/or the mineral salt lessthan 10 ppm shows a tendency of making difficult efficient removal ofthe unreacted polyfunctional amine component from the semipermeablemembrane. On the other hand, the concentration exceeding 50% by weighthas a great influence on performance of the semipermeable membrane, andshows a tendency for permeation flux to deteriorate.

The water-soluble organic substance is not in particular limited, aslong as it does not give adverse effect on membrane performance, and thesubstance include, for example, monohydric alcohols, such as methylalcohol, ethyl alcohol, n-propyl alcohol, and isopropyl alcohol;polyhydric alcohols, such as ethylene glycol, triethylene glycol, andglycerin; ethers, such as ethylene glycol monomethyl ether, ethyleneglycol monoethyl ether, and ethylene glycol monobutyl ether; polarsolvents, such as dimethylformamide, dimethylacetamide, andn-methylpyrrolidone.

In view of the suppression effect of deterioration of removalperformance and membrane performance of the unreacted polyfunctionalamine component, the concentration of the water-soluble organicsubstance in the aqueous solution can be suitably adjusted for everymaterial to be used, and it is approximately 1 to 90% by weight, morepreferably 10 to 80% by weight, and especially preferably 20 to 50% byweight. Less than 1% by weight of the concentration of the water solubleorganic substance shows a tendency of making difficult efficient removalof the unreacted polyfunctional amine component from the semipermeablemembrane. On the other hand, the concentration exceeding 90% by weighthas a great influence on performance of the semipermeable membrane, andshows a tendency for permeation flux to deteriorate.

3) A method of, first of all, making the composite semipermeablemembrane contact with a solution including the water soluble organicsubstance, then making the semipermeable membrane contact with anaqueous solution containing the acidic substance to wash the membrane.

A reversed order of contact with solutions cannot fully remove theunreacted polyfunctional amine component. Firstly conducted contact ofthe composite semipermeable membrane with the solution containing thewater soluble organic substance can accelerate hydrophilization andswelling of the membrane. Therefore, this process allows quickpermeation of the aqueous solution including the acidic substance to aninner portion of the membrane in the subsequent contact treatment, andcan increase washing effect.

In consideration of the suppression effect of deterioration of removalperformance and membrane performance of the unreacted polyfunctionalamine component, the concentration of the water soluble organicsubstance in the solution can be suitably adjusted for every materialsto be used, and usually, it is 1 to 100% by weight, preferably 10 to 80%by weight, and more preferably 20 to 50% by weight. It is especiallypreferred to use the aqueous solution having the above describedconcentration. The concentration of the water soluble organic substanceless than 1% by weight shows a tendency of making difficult efficientremoval of the unreacted polyfunctional amine component from thesemipermeable membrane.

The concentration of the acidic substance in the aqueous solution ispreferably 10 ppm to 50% by weight, more preferably 50 ppm to 20% byweight, and especially preferably 1 to 10% by weight. The concentrationof the acidic substance less than 10 ppm shows a tendency of makingdifficult efficient removal of the unreacted polyfunctional aminecomponent from the semipermeable membrane. On the other hand, theconcentration exceeding 50% by weight has a great influence on theperformance of the semipermeable membrane.

In the membrane washing methods 1) to 3) described above, examples ofthe method of contacting the solution to the composite semipermeablemembrane include all methods, such as a dipping, a pressurized waterflow, a spray, an application, and a showering, and the dipping and thepressurized water flow methods are preferably used in order to obtainsufficient effect of contacting.

The contact period of time is not limited at all within a rangeacceptable by an allowable content of the unreacted polyfunctional aminecomponent in the composite semipermeable membrane after the membranewashing treatment, and manufacturing restrictions, and any period oftime may be adopted. Although the contact period of time cannotnecessarily be specified, it is usually several seconds to tens ofminutes, and preferably 10 seconds to 3 minutes. Since the amount ofremoval of the unreacted polyfunctional amine component reaches anequilibrium, removing effect does not necessarily improve even withlonger contact period of time. When the contact period of time isexcessively lengthened, there is conversely shown a tendency for themembrane performance and manufacturing efficiency to deteriorate.Although the contact temperature in particular will not be limited aslong as the solution is in a temperature range allowing existence as aliquid, from a view point of removing effect of the unreactedpolyfunctional amine component, of prevention of the membrane fromdeterioration, and of easiness of treatment etc. the contact temperatureis preferably 10 to 90° C., more preferably 10 to 60° C., and especiallypreferably 10 to 45° C.

In the contact of the solution by the pressurized water flow method, thepressure is not in particular limited, as long as the pressure in use ofthis solution with respect to the semipermeable membrane is in a rangeacceptable by the semipermeable membrane and the physical strength ofthe members and the equipment for pressure application. The pressurizedwater flow is preferably performed at 0.1 to 10 MPa, and more preferablyat 1.5 to 7.5 Mpa. The pressurized water flow at a pressure less than0.1 Mpa shows a tendency of extending the contact period of time, inorder to obtain necessary effect. And when exceeding 10 Mpa, compactioncaused by the pressure is apt to decrease the permeation flux.

The present invention needs application of treatment to the poroussupport with additives by inclusion of at least one kind of theadditives selected from the group consisting of antioxidants,antibacterial agents, antifungal agents, and moisturizers. Methods forinclusion of the additives in the porous support is not in particularlimited, and preferred is a method for contact of an aqueous solutionincluding at least one kind of additives selected from the groupconsisting of antioxidants, antibacterial agents, antifungal agents, andmoisturizers to a face that does not have the skin layer of the poroussupport of the unwashed or washed composite semipermeable membraneproduced by the method described above.

The antioxidant include, for example, sulfites, such as sodium sulfite,sodium hyposulfite, sodium bisulfite, potassium sulfite, potassiumhydrogen hyposulfite; sulfur dioxide; citrates, such as isopropylcitrate; and Vitamins C, such as ascorbic acid, alkyl ascorbate, andsodium ascorbate.

The antibacterial agents and antifungal agents include, for example,silver based compounds; copper based compounds; photocatalyticcompounds; chitosans; and catechins, such as catechin, epicatechin,gallocatechin, epigallocatechin, catechin gallate, epicatechin gallate,gallocatechin gallate, and epigallocatechin gallate.

The moisturizer includes, for example, organic acid alkali metal salts,such as sodium acetate, potassium acetate, sodium lactate, potassiumlactate, sodium glutamate, and potassium glutamate; organic acidalkaline earth metal salts, such as magnesium acetate, calcium acetate,magnesium lactate, calcium lactate, magnesium glutamate, and calciumglutamate; inorganic acid alkaline metal salts, such as sodiumhydrogencarbonate, potassium hydrogencarbonate, sodium carbonate,potassium carbonate, disodium monohydrogen phosphate, dipotassiummonohydrogen phosphate, monosodium dihydrogen phosphate, monopotassiumdihydrogen phosphate, sodium phosphate, potassium phosphate; inorganicacid alkaline earth metal salts, such as magnesium hydrogencarbonate,calcium hydrogencarbonate, magnesium carbonate, calcium carbonate,magnesium primary phosphate, calcium primary phosphate, magnesiumsecondary phosphate, calcium secondary phosphate, magnesium tertiaryphosphate, calcium tertiary phosphate: alkali metal halides, such assodium chloride; alkali earth metal halides, such as magnesium chloride;surfactants, such as sodium lauryl sulfate, lauryl potassium sulfate,sodium alkyl benzene sulfonate, and potassium alkylbenzene sulfonate;saccharides, such as glucose and saccharose; amino acids, such asglycine and leucine etc.

The concentration of the additives in the aqueous solution is not inparticular limited, and it is preferably 100 ppm to 30% by weight, andmore preferably 500 ppm to 10% by weight. The concentration of theadditives less than 100 ppm does not sufficiently exhibit effect forcontrolling deterioration in water permeability and salt-blocking rateafter long-term storage, showing a tendency of requiring a longerprocessing time. On the other hand, the concentration of additivesexceeding 30% by weight causes increase in costs, showing a tendency ofgiving an adverse effect to film performance.

Methods for contacting the aqueous solution containing the additives inthe porous support includes, for example, application method, sprayingmethod of the aqueous solution containing the additives, or contactmethod with a vapor of the additives, etc., and is not limited to them,and publicly known method are employable. Alternatively, in the case ofimmersion of the composite semipermeable membrane in the aqueoussolution containing the additives, immersion of the compositesemipermeable membrane is performed in a state where the skin layer isclosely contacted to a roll, in order to realize inclusion of most ofthe additives in the porous support.

In the case of application of an aqueous solution containing additivesto the composite semipermeable membrane, the aqueous solution ispreferably applied to only the surface of the porous support in order toprevent deterioration of performance of the skin layer.

Although the temperature of the aqueous solution is not in particularlimited as long as the solution is in a temperature range that allowsexistence of the aqueous solution as a liquid, from viewpoints ofexhibition of target effect, prevention of the membrane fromdeterioration, easiness of treatment, etc., it is preferably 10 to 90°C., more preferably 10 to 60° C., especially preferably 10 to 45° C.

Excessive aqueous solution may be removed after contact of the aqueoussolution containing the additives in the composite semipermeablemembrane by the above-described method. Removal methods include, forexample, a contact type removal method with blades, made of plastics orrubbers, a non-contact type removal method with air knife, etc.

The content of the additives in the porous support may be suitablyadjusted based on the kinds of additives, the grade of targeted effectetc., and, it is preferably 1 mg/m² to 100 g/m², and more preferably 10mg/m² to 10 g/m² for sufficient expression of the targeted effect. Thecontent of the additives less than 1 mg/m² shows a tendency of failingto exhibit sufficient deterioration inhibitory effect of the waterpermeability and the salt-blocking rate after long-term storage. On theother hand, the content exceeding 100 g/m² does not vary deteriorationinhibitory effect of water permeability and salt-blocking rate afterlong-term storage for the increase of content, leading to possible lackof stability of water quality of the target compound caused by elutionof the additives.

It is necessary for the porous support to have 95% by weight or more ofcontent of the additives with respect to the whole compositesemipermeable membrane, and preferably 96% by weight or more.

The amount and content of the additives included in the whole compositesemipermeable membrane and porous support may be measured by thefollowing method.

(Separate Method)

A composite semipermeable membrane is cut into a predetermined size andis separated into a skin layer and a porous support. As a method ofseparation, for example, a method wherein a pressure sensitive adhesivetape attached on the surface of the skin layer of the compositesemipermeable membrane having a size of 50 mm×50 mm is separated afterslight friction may be mentioned. By this method, the skin layer and amicroporous layer on an uppermost surface of the porous support isseparated together with the pressure sensitive adhesive tape. Theremaining portion that does not attach to the tape is defined as aporous support. Subsequently, the separated porous support is boiled ina specified amount of pure water, the obtained extracted liquid isanalyzed using publicly known methods of analysis, such as ionchromatograph analysis, GC analysis, absorption spectrometry, andrefractive index analysis to determine the amount of the additives inthe porous support. Furthermore, the composite semipermeable membranecut into a predetermined size is also measured for the amount ofadditives in a similar way. The two obtained values are substituted forthe following expression, and the content of additives in the poroussupport is calculated.

Contain rate (%)=[(contain in porous support)/(contain in compositesemipermeable membrane)]×100

In the present invention, subsequently, the composite semipermeablemembrane, to which the treatment with additives is applied with themethod described above, may be dried to obtain a dried compositesemipermeable membrane.

The temperature of drying treatment is not in particular limited, and itis preferably 20 to 150° C., and more preferably 40 to 130° C. Thetemperature less than 20° C. needs an excessively long drying treatmentperiod, and likely gives insufficient drying. The temperature exceeding150° C. shows a tendency to cause decrease of membrane performance dueto structural change of the membrane caused by heat.

The period of the drying treatment is not in particular limited, and itis preferred that drying is performed until the amount of solvents inthe dried composite semipermeable membrane is 5% by weight or less.

In addition, in the case of production of a dry spiral element, themembrane may be processed into a spiral shape in any stage fromproduction of the above-described skin layer to drying treatment. Indetail, the composite semipermeable membrane may be processed into aspiral shape before the washing treatment of the membrane to produce amembrane unit. Alternatively, the composite semipermeable membrane maybe processed into a spiral shape after treatment with additives toproduce the membrane unit, and the composite semipermeable membrane maybe processed into a spiral shape before the drying treatment to producethe membrane unit.

Furthermore, the membrane unit may be produced by simultaneousapplication of the washing treatment and the treatment with additives tothe produced membrane unit. The same method as the one described abovemay be mentioned as the treatment method.

The dried composite semipermeable membrane and dry spiral elementproduced by such a method have extremely small content of unreactedcomponents. A permeated liquid separated and refined or a targetcompounds condensed by using the composite semipermeable membrane, etc.,includes extremely small amount of impurities, and has a high purity.The dried composite semipermeable membrane and the dry spiral element ofthe present invention have outstanding workability and preservabilitybecause it is a dry type. Furthermore, although the dried compositesemipermeable membrane and the dry spiral element of the presentinvention are a dry type, they exhibit water permeability andsalt-blocking rate equivalent to that of the wet type compositesemipermeable membrane and spiral element, causing no deterioration ofperformance after long term storage.

For improvement in salt-blocking property, water permeability,anti-oxidation agent property, etc., of the dried compositesemipermeable membrane or dry spiral element, various conventionallypublicly known treatments may be applied.

EXAMPLE

The present invention will, hereinafter, be described with reference toExamples, but the present invention is not limited at all by theseExamples.

(Measurement of Permeation Flux and Salt-Blocking Rate)

A dried composite semipermeable membrane produced with a shape of a flatfilm is cut into a predetermined shape and size, and is set to a cellfor flat film evaluation. An aqueous solution containing NaCl of about1500 mg/L and adjusted to a pH of 6.5 to 7.5 with NaOH was forced tocontact to a supply side, and a permeation side of the membrane at adifferential pressure of 1.5 MPa at 25° C. A permeation velocity and anelectric conductivity of the permeated water obtained by this operationwere measured for, and a permeation flux (m³/m²·d) and a salt-blockingrate (%) were calculated. The correlation (calibration curve) of theNaCl concentration and the electric conductivity of the aqueous solutionwas beforehand made, and the salt-blocking rate was calculated by afollowing equation.

Salt-blocking rate (%)={1−(NaCl concentration [mg/L] in permeatedliquid)/(NaCl concentration [mg/L] in supply solution)}×100

(Measurement of Content and Content Rate of Additives)

A prepared dried composite semipermeable membrane was cut into a size of1 cm×3 cm to obtain samples A and B. A pressure sensitive adhesive tape(made by NITTO DENKO CORPORATION, No. 31-B) was attached on the surfaceof the skin layer of sample A, and the pressure sensitive adhesive tapewas separated after light friction. The skin layer and the microporouslayer on the uppermost surface of the porous support were removedtogether with the pressure sensitive adhesive tape. Subsequently, theseparated porous support was immersed into 50 cc of pure water, and wasboiled at 120° C. for 1 hour in a sealed state. The obtained extractedliquid was subjected to analysis with ion chromatography to obtain anamount of additives in the extracted liquid. Determination of theadditives was performed by comparison to a calibration curve preparedusing standard solutions beforehand prepared to several kinds ofprescribed concentrations. Measurement conditions are shown as follows.

Analyzer: Ion chromatograph, manufactured by DIONEX CORPORATION, DX-320

Isolation column: Ion Pac AS15 (4 mm×250 mm)

Guard column: Ion Pac AG15 (4 mm×50 mm)

Detector: Conductometrical detector

Eluate: KOH 2 mM→10 mM

Eluate flow rate: 1.2 mL/min

Specimen injection: 50 μL

Furthermore, sample B was immersed into 50 cc of pure water, and wasboiled for 1 hour at 120° C. in a sealed state. Subsequently, theextracted liquid was subjected to analysis under the same conditions asdescribed above to obtain an amount of additives in the extractedliquid. The two obtained value were substituted for the followingexpression, and the content rate of the additives in the porous supportwas calculated.

Content rate(%)=[(content in porous support)/(content in compositesemipermeable membrane)]×100

Production Example 1 Production of Porous Support

A dope for manufacturing a membrane containing 18% by weight of apolysulfone (produced by Solvay, P-3500) dissolved inN,N-dimethylformamide (DMF) was uniformly applied so that it might give200 μm in thickness in wet condition on a nonwoven fabric base material.Subsequently, it was immediately solidified by immersion in water at 40to 50° C., and DMF as a solvent was completely extracted by washing.Thus a porous support having a polysulfone microporous layer wasproduced on the nonwoven fabric base material.

Example 1

An aqueous solution of amines containing 3% by weight ofm-phenylenediamine, 3% by weight of triethylamine, and 6% by weight ofcamphorsulfonic acid was applied to the porous support, and then anexcessive amount of the amine aqueous solution was removed to form acovering layer of the aqueous solution. Subsequently, an isooctanesolution containing 0.2% by weight of trimesic acid chlorides wasapplied to the surface of the covering layer of the aqueous solution.Then, the excessive solution was removed, and the material was keptstanding for 3 minutes in a hot air dryer at 120° C. to form a skinlayer containing a polyamide resin on the porous support, an unwashedcomposite semipermeable membrane was obtained. After that time, theunwashed composite semipermeable membrane was immersed for 10 minutes at50° C. in pure water for membrane washing treatment to produce a washedcomposite semipermeable membrane. Subsequently, a sodium acetate aqueoussolution (concentration: 5% by weight) was applied to the surface (aface which does not have a formed skin layer) of the porous support ofthe washed composite semipermeable membrane under a condition of 30cc/m² for treatment with additives. And treated composite semipermeablemembrane stood to remove the excessive sodium acetate aqueous solution,and then was kept standing for 5 minutes in a hot air dryer at 80° C.,finally producing a dried composite semipermeable membrane.

Example 2

A dried composite semipermeable membrane was produced in the same manneras in example 1, except for using a sodium lactate aqueous solution(concentration: 5% by weight) instead of the sodium acetate aqueoussolution in example 1.

Example 3

A dried composite semipermeable membrane was produced in the same manneras in example 1, except for using a sodium hydrogen carbonate aqueoussolution (concentration: 5% by weight) instead of the sodium acetateaqueous solution in example 1.

Example 4

A composite semipermeable membrane was produced in the same manner as inexample 1, except for using a sodium bisulfite aqueous solution(concentration: 5% by weight) instead of the sodium acetate aqueoussolution, and not drying after treatment with additives in example 1.

Example 5

A dried composite semipermeable membrane was produced in the same manneras in example 1, except for using a sodium bisulfite aqueous solution(concentration: 5% by weight) instead of the sodium acetate aqueoussolution in example 1.

Comparative Example 1

A washed composite semipermeable membrane was produced in the samemanner as in example 1. Subsequently, the washed composite semipermeablemembrane was immersed in a sodium acetate aqueous solution(concentration: 5% by weight) for 1 minute at 25° C., and treatment withadditives was applied. Then, the treated composite semipermeablemembrane stood and thus the excessive sodium acetate aqueous solutionwas removed, and then was kept standing for 5 minutes in a hot air dryerat 80° C. to produce a dried composite semipermeable membrane.

Comparative Example 2

A washed composite semipermeable membrane was produced in the samemanner as in example 1. Subsequently, a sodium acetate aqueous solution(concentration: 5% by weight) 25° C. was applied on the surface of theskin layer of the washed composite semipermeable membrane under acondition of 30 cc/m², the surface was uniformly smoothed using a PETfilm and then treatment with additives was applied. Then, the treatedcomposite semipermeable membrane stood and thus the excessive sodiumacetate aqueous solution was removed, and next was kept standing for 5minutes in a hot air dryer at 80° C. to produce a dried compositesemipermeable membrane.

Comparative Example 3

A dried composite semipermeable membrane was produced in the same manneras in example 1, except for not performing treatment with additives inexample 1.

Comparative Example 4

A washed composite semipermeable membrane was produced in the samemanner as in example 1. Appearance of mold in the skin layer wasobserved after storage for one week of the washed compositesemipermeable membrane.

Comparative Example 5

An unwashed composite semipermeable membrane was produced in the samemanner as in example 1.

TABLE 1 Content of additives (mg/m²) Initial Performance Whole Contentof performance one week after Condition composite additives toPermeation Permeation of semipermeable Porous porous Salt-blocking FluxSalt-blocking Flux membrane Additive membrane support support (%) rate(%) (m³/m² · d) rate (%) (m³/m² · d) Example 1 Washed, Sodium 790 78098.7 99.3 0.8 99.3 0.8 dry acetate Example 2 Washed, Sodium 1050  1020 97.1 99.5 0.9 99.6 0.8 dry lactate Example 3 Washed, Sodium 570 550 96.599.3 0.6 99.2 0.6 dry hydrogen carbonate Example 4 Washed, Sodium 580570 98.3 99.4 0.6 99.3 0.6 wet bisulfite Example 5 Washed, Sodium 600580 96.7 99.5 1.0 99.5 1.0 dry bisulfite Comparative Washed, Sodium 820740 90.2 98.9 0.9 98.7 0.8 Example 1 dry acetate Comparative Washed,Sodium 660 590 89.4 97.9 1.1 97.1 1.2 Example 2 dry acetate ComparativeWashed, — — — — Measurement impossible (permeation flux <0.1) Example 3dry Comparative Washed, — — — — 99.5 0.9 99.1 0.7 Example 4 wetComparative Unwashed, — — — — 99.5 0.9 99.0 1.4 Example 5 dry

As is clearly shown in table 1, a composite semipermeable membranehaving water permeability and salt-blocking rate without deteriorationafter long-term storage may be obtained by mainly including specificadditives mainly in a porous support.

1. A composite semipermeable membrane having a skin layer formed on thesurface of a porous support, the skin layer comprising a polyamide resinobtained by interfacial polymerization of a polyfunctional aminecomponent and a polyfunctional acid halide component, wherein the poroussupport contains at least one kind of additive selected from the groupconsisting of an antioxidant, an antibacterial agent, an antifungalagent, and a moisturizer in an amount of 95% by weight or more withrespect to the whole composite semipermeable membrane.
 2. The compositesemipermeable membrane according to claim 1, wherein the compositesemipermeable membrane is a dried composite semipermeable membrane. 3.The composite semipermeable membrane according to claim 1, wherein themoisturizer is an organic acid metal salt and/or an inorganic acid metalsalt.
 4. The composite semipermeable membrane according to claim 3,wherein the organic acid metal salt is at least one kind of organic acidalkali metal salt selected from the group consisting of an alkali metalacetate, alkali metal lactate, and alkali metal glutamate.
 5. Thecomposite semipermeable membrane according to claim 3, wherein theinorganic acid metal salt is at least one kind of inorganic acid alkalimetal salt selected from the group consisting of an alkali metalhydrogencarbonate, dialkali metal monohydrogen phosphate, and monoalkalimetal dihydrogen phosphate.
 6. A process for producing a compositesemipermeable membrane comprising: forming a skin layer including apolyamide resin obtained by reaction between a polyfunctional aminecomponent and a polyfunctional acid halide component on the surface of aporous support; and performing a treatment with additives onto theporous support by contact of an aqueous solution including at least onekind of additives selected from the group consisting of an antioxidant,an antibacterial agent, an antifungal agent, and a moisturizer, to aface without the skin layer of the porous support.
 7. The compositesemipermeable membrane according to claim 2, wherein the moisturizer isan organic acid metal salt and/or an inorganic acid metal salt.
 8. Thecomposite semipermeable membrane according to claim 7, wherein theorganic acid metal salt is at least one kind of organic acid alkalimetal salt selected from the group consisting of an alkali metalacetate, alkali metal lactate, and alkali metal glutamate.
 9. Thecomposite semipermeable membrane according to claim 7, wherein theinorganic acid metal salt is at least one kind of inorganic acid alkalimetal salt selected from the group consisting of an alkali metalhydrogencarbonate, dialkali metal monohydrogen phosphate, and monoalkalimetal dihydrogen phosphate.
 10. The composite semipermeable membraneaccording to claim 1, wherein the porous support contains an antioxidantselected from the group consisting of sodium sulfite, sodiumhyposulfite, sodium bisulfite, potassium sulfite, potassium hydrogenhyposulfite, sulfur dioxide, isopropyl citrate, ascorbic acid, alkylascorbate, and sodium ascorbate.
 11. The composite semipermeablemembrane according to claim 1, wherein the porous support contains anantibacterial agent selected from the group consisting of a silver basedcompound, a copper based compound, a photocatalytic compound, achitosan, and a catechin.
 12. The composite semipermeable membraneaccording to claim 1, wherein the content of the additive(s) in theporous support is 1 mg/m² to 100 g/m².
 13. The process of claim 6,further comprising drying the treated composite semipermeable membrane.14. The process of claim 6, wherein concentration of the additives inthe aqueous solution is 100 ppm to 30% by weight.